1. Field of the Invention
This invention relates to mechanisms which automatically track the sun in its apparent westward motion across the sky between sunrise and sunset. More particularly it relates to self-contained solar energy-powered tracking means for driving devices such as solar collectors, reflectors, shutters and the like in response to the sun's diurnal movement.
2. Prior Art
Man's fascination with the sun has been traced to the dawn of history and has lead to some notable achievements, particularly during the past 50 years, in the development of devices for collecting and utilizing energy from this seemingly limitless source. Gradual but accelerating recognition, especially during the last decade, of the finite limit to the world's supply of fossil fuels and the lack of presently available alternative sources of energy has cast a sense of urgency over the need to put these devices into immediate widespread use.
Relatively efficient solar furnaces, heaters, energy convertors and the like have been designed and tested, and many are in actual use, but their mass application awaits the solution of a well known but heretofore never satisfactorily resolved problem. To utilize solar radiation effectively, it must either be concentrated by means of a convex or parabolic mirror or with some system of lenses, or allowed to impinge directly on the area to be heated or irradiated. Regardless of the type of system that is used, it has been demonstrated that for satisfactory results the collector must be mounted and driven to follow the sun's motion. The key to the efficient operation of any solar collector lies in maintaining the collector's reflective surface perpendicular to the incident radiation as long as possible during the diurnal transit.
In recognition of this fact the prior art contains a variety of solar tracking devices. In one of the earliest of these a weighted rope wound around the collector's axle is allowed to unwind at a controlled rate such that the angular rotation of the axle approximates that of the sun across the sky. Over the intervening centuries far more sophisticated clockwork mechanisms have been developed to accomplish the same purpose. The advent of the synchronous motor and servo-technology led to the development of tracking systems utilizing shaded bimetallic thermoregulators, silicon photocells and fluid-mechanical switches to actuate a tracking motor. Another class of tracking devices employs bimetallic springs or levers to power a variety of mechanical driving means. Still another class uses some form of piston operated fluid-mechanical drive.
While many of these devices are useful and some, in fact, are extremely accurate, by and large their advantages are more than offset by several disadvantages. The purpose of the subject invention is to provide a fully self-contained and entirely automatic solar tracking device which overcomes all of those disadvantages. More particularly, an object of the invention is to provide a tracking device which can be produced and operated inexpensively and which requires little maintenance and can be maintained easily. Another object is to provide a device of this general type capable of tracking the sun with a reasonable degree of precision throughout the entire diurnal transit and which automatically recycles itself at the end of that transit in readiness for the following diurnal cycle. Yet another object is to provide a solar tracking mechanism which responds well to changes in incident radiation.
Up to this point the discussion has been directed toward tracking devices for use on solar energy collectors. It will be understood that many of the considerations applicable to devices used to collect the sun's energy are equally applicable to devices used to interdict solar radiation. By way of example, in architecture the use of slats or louvres to control the incidence of solar radiation on the windows and walls of buildings is well known. The advantages of a device which would allow such slats or louvres to track the sun automatically are likewise well known. By and large the criteria for such a device are the same as those for a solar tracking mechanism used to control a solar energy collector. Accordingly, it is still another object of the invention to provide a solar tracking mechanism of the type previously discussed, which can be utilized in a variety of applications including solar energy collection and solar radiation interdiction.
For most applications, a tracking device responsive to the sun's diurnal motion across the sky is quite adequate. For others, however, compensation must be made for the annual movement of the sun in the ecliptic, or apparent yearly path in the sky northward and southward through the celestial equator. With such latter applications in mind, it is another object of the subject invention to provide a tracking device capable of automatically compensating for the constantly changing zenith distance or "high point" of the sun from day to day.